Mammals with naturally occurring or experimentally induced primary autochthonous cancer are being studied as guides to the immunotherapy of human cancer. It is hoped that these guides will provide information more relevant to the treatment of human cancer than that derived from studies with transplanted tumors. Cattle with ocular squamous cell carcinoma ("cancer eye") have been treated successfully by the injection of BCG cell wall vaccine directly into the tumor. Primary autochthonous tumors of rats and humans are also being studied.